The knee joint basically consists of the bone interface of the distal end of the femur and the proximal end of the tibia. Appearing to cover or at least partially protect this interface is the patella, which is a sesamoid bone within the tendon of the long muscle (quadriceps) on the front of the thigh. This tendon inserts into the tibial tuberosity and the posterior surface of the patella is smooth and glides over the femur.
The femur is configured with two knob like processes (the medial condyle and the lateral condyle) which are substantially smooth and which articulate with the medial plateau and the lateral plateau of the tibia, respectively. The plateaus of the tibia are substantially smooth and slightly cupped thereby providing a slight receptacle for receipt of the femoral condyles.
When the knee joint is damaged whether as a result of an accident or illness, a prosthetic replacement of the damaged joint may be necessary to relieve pain and to restore normal use to the joint. Typically the entire knee joint is replaced by means of a surgical procedure that involves removal of the surfaces of the corresponding damaged bones and replacement of these surfaces with prosthetic implants. This replacement of a native joint with a prosthetic joint is referred to as a primary total-knee arthroplasty.
On occasion, the primary knee prostheses fails. Failure can result from many causes, including wear, aseptic loosening, osteolysis, ligamentous instability, arthrofibrosis and patellofemoral complications. When the failure is debilitating, revision knee surgery may be necessary. In a revision, the primary knee prosthesis is removed and replaced with components of a revision prosthetic knee system.
Knee implant systems for both primary and revision applications are available from a variety of manufacturers, including DePuy Orthopaedics, Inc. of Warsaw, Ind. DePuy and others offer several different systems for both primary and revision applications. For example, DePuy Orthopaedics offers the P.F.C. SIGMA® Knee System, the LCS® Total Knee System, and the S-ROM Modular Total Knee System. These orthopaedic knee systems includes several components, some appropriate for use in primary knee arthroplasty and some appropriate for use in revision surgery.
DePuy Orthopaedics also offers other orthopaedic implant systems for other applications. One such system is the LPS System. The LPS System is provided for use in cases of severe trauma and disease. In such cases, the trauma or disease can lead to significant amounts of bone loss. The LPS System provides components that can replace all or significant portions of a particular bone, such as the femur. The DePuy LPS System is described more fully in U.S. patent application Ser. No. 10/135,791, entitled “Modular Limb Preservation System”, filed Apr. 30, 2002 by Hazebrouck et al. (U.S. Pat. Pub. No. 2003-0204267), which is incorporated by reference herein in its entirety.
In some patients, the metaphysis of the bone near the joint presents cavitary defects that are not completely filled by standard knee implants. The presence of such metaphyseal defects can result in loosening of the prosthetic implant over time, compromising the stability of the prosthetic implant and frequently requiring revision of the prosthetic implant.
To fill metaphyseal cavitary defects, knee systems with modular metaphyseal sleeves have been provided. Such sleeves are illustrated, for example, in: U.S. Pat. Pub. No. 2010/0114323, entitled “Knee Prosthesis Kit with Winged Sleeves and Milling Guide;” U.S. Pat. Pub. No. 2006/0030945A1, entitled “Modular Orthopaedic Implant System With Multi-Use Stems;” U.S. Pat. No. 7,799,085, entitled “Modular Implant System With Fully Porous Coated Sleeve;” U.S. Pat. No. 7,291,174, entitled “Prosthetic Tibial Component With Modular Sleeve;” U.S. Pat. No. 6,171,342, entitled “Medical Fastening System;” U.S. Pat. No. 5,824,097, entitled “Medical Fastening System;” U.S. Pat. No. 5,782,921, entitled “Modular Knee Prosthesis;” and U.S. Pat. No. 4,634,444, entitled “Semi-Constrained Artificial Joint.” Such sleeves have been used in commercially available prosthetic knee implant systems, such as the P.F.C. SIGMA.® Knee System, the LCS® Total Knee System, the S-ROM Modular Total Knee System and the LPS System, all available from DePuy Orthopaedics, Inc. of Warsaw, Ind.
Modular sleeves have also been used in hip implant systems, as illustrated, for example, in: U.S. Pat. No. 6,264,699, entitled “Modular Stem and Sleeve Prosthesis;” and U.S. Pat. No. 4,790,852, entitled “Sleeves for Affixing Artificial Joints to Bone.” Such hip sleeves have been used in commercially available prosthetic hip implant systems, such as the S-ROM hip systems, available from DePuy Orthopaedics, Inc. of Warsaw, Ind.
The disclosures of all of the above patent applications and patents are incorporated by reference herein in their entireties.
In knee systems with modular metaphyseal sleeves, the conventional shape of many of the sleeves is generally an elliptical cone with a large ellipse profile close to the joint line tapering down to a smaller elliptical or circular profile at the termination of the component distal to the joint line. Generally, the sleeves have a terraced or stepped outer surface and an inner channel for frictional fixation to another component. This geometry fills cavitary defects in the metaphysis, allows for a wider surface area for load transfer through the joint and provides rotational stability for the articulating components of the prosthesis.
The outer surface of the sleeve is supported by solid bony structure or the bone bed. In the case of the distal femur, patient anatomy and the condition of the bone, particularly in a revision surgery, may require that the distal femur be resected to a more proximal level. Implanting a prosthetic distal femoral component and sleeve at this more proximal level may elevate the joint line (that is, the line defined by the articulation of the articular surfaces of the distal femoral component and proximal tibial component). Elevation of the joint line may adversely affect performance of the prosthetic knee system: the positions of the collateral ligament attachments to the femur relative to the joint line may impact knee kinematics, the articulation of the patella against the femoral component will be impacted, and the function of the extensor mechanism will also be impacted.
Prosthetic knee implant systems have commonly included femoral augments for use on the distal and posterior bone-facing surfaces of the femoral implant components. Examples of such augments are disclosed in U.S. Pat. Nos. 6,005,018 and 5,984,969, which are incorporated by reference herein in their entireties. Such components serve to augment the inferior and posterior portions of the femoral component to add additional thickness to compensate for the lack of sufficient boney tissue, allowing the joint line to be distalized. However, with the femoral component so distalized, the metaphyseal sleeve used with the femoral component may no longer be optimally seated on a healthy bone bed. To compensate, surgeons may sometimes opt to use a larger size of metaphyseal sleeve. Because of differences in the geometries of differently-sized metaphyseal sleeves, changing to a larger size requires that the surgeon prepare the bone cavity a second time so that the cavity will accept the geometry of the larger size of metaphyseal sleeve.
Accordingly, a need exists for a knee prosthesis system that allows the surgeon the flexibility to optimize the position of the joint line while also allowing for a metaphyseal sleeve to be efficiently and optimally positioned on a healthy bone bed.